The microscope

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					           The microscope
• First developed in the 1600’s in Europe.
• Gave rise to the Cell Theory in 1839
• The Cell Theory states:
• (1) All organisms are composed of one or
  more cells
• (2) The cell is the structural unit of life
• (3) Cells can arise only by division from a
  preexisting cell
 What can a Microscope tell us
• Allows user to view the morphology of a
  cell
• Typically seen are nucleus, plasma
  membrane, cell wall and chloroplasts in
  plants
• Cells are viewed as two dimensional even
  though cells are really three dimensional
• Difficult to view details in cell because a
  cell lacks color
• Chemical dyes are used to give cells color
  and to make parts of a cell visible
• Dyes can be used to stain DNA, proteins,
  specific cellular structures
• Problem light microscope can resolve
  features who size is not less than 0.2 mm
• Resolution is the ability to discern two
  objects as being separate
• Unfortunately, most organelles in a cell are
  less than 0.2 mm in size
• In the 1950’s the transmission electron
  microscope was invented.
• This microscope has a resolution of 10 –
  15 Angstroms. (One Angstrom is ten
  thousand mm)
• This allows organelles to be viewed.
• Yet in spite of the electron microscope the
  function of a cell is not revealed!
• The problem is not the microscope but the
  information that it yields
• The function of a cell is revealed through
  biochemistry.
• In order for a cell to be alive it must be
  acquire and use energy
• Possess a genetic code and have a way to
  use it.
• Cell must be able to replicate
• Respond to stimuli
• Self-regulation
     Eukaryote vs Prokaryote
• Using a light microscope it is possible to
  determine if a cell has a nucleus or not.
• Those cells who do have a nucleus are
  call eukaryotes and those without a
  nucleus are prokaryotes.
• Typically, prokaryotes are bacteria and the
  cells do not work together
• Eukaryotes work together and comprise
  complex organisms like us.
• Eukaryotes are specialized cells that
  require resources from other cells to
  survive.
• Typically eukaryotes have much greater
  energy needs than prokaryotes.
• To satisfy the energy needs as well as the
  specialization eukaryotes have organelles.
• Organelles are membrane bound
  structures that perform a specific task.
Prokaryotes are not evolutionay
   ancestors of eukaryotes
• Eukaryotes and prokaryotes are very
  different.
• Prokaryotes have a single RNA
  polymerase
• Eukaryotes have three
• Prokaryotes do not have RNA splicing
• The ribosomes in prokaryotes and
  eukaryotes are different
            The archea
• Resemble bacteria found in extreme
  environments on the earth
• Examples include methanogens which
  consume methane.
• We will talk more about organelles later in
  the course
  Infectious agents that are not
               cells
• Viruses, viroids, and prions are infectious
  agents, but are not cells
• In fact, most people would agree that
  these infectious agents are not alive.
• Why?????
• As previously mentioned a cell must be
  able to perform specific processes to be
  considered alive

				
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